1. Field of the Invention
This invention relates to an image detector for sensing radiation.
2. Description of the Related Art
EP-A-0588397 describes an image detector for sensing radiation, in particular x-ray radiation, which comprises an array of sensors formed from layers of material provided on a substrate and separated from a biasing electrode by a radiation conversion layer in which charge carriers are generated in response to incident radiation. Each sensor has a collecting electrode for collecting charge carriers generated in the radiation conversion layer, a capacitor for storing charge and a switching element having at least first and second electrodes. One of the first and second electrodes of the switching element of each sensor is coupled to the collecting electrode for enabling charge stored at the sensor to be read out. Each collecting electrode extends laterally beyond the associated switching element to form the associated capacitor with an underlying reference electrode. In the examples described in EP-A-0588397, the reference electrode is separated from the collecting electrode by the same insulating layer as that used to form the gate insulating layer of the thin film transistors forming the switching element. Accordingly, the thickness of this layer cannot be varied without affecting the threshold characteristics of the switching elements which may, under certain circumstances, not be desirable.